Hydraulic fracturing, or simply fracturing of subterranean formation is aimed to creation of a high-conductive path (the fracture) through a reservoir (oil-bearing stratum) in order to stimulate hydrocarbons (oil and gas) inflow into a wellbore includes injection of fracturing fluid comprising proppant (also referred to as propping agent) particles with forming a pack within the treated reservoir. Such a proppant pack penetrates through the reservoir, while its permeability is much higher than that of the reservoir itself. Nevertheless, the permeability of an actual proppant pack created in the formation is lower compared to the expected permeability (of clean proppant pack) due to numerous nuance including the following:
1. Proppant embedment into fracture walls.
2. The residuals of fracturing fluid (gel fluid) partially blocking pores and creating a filter cake on the walls of fracture.
3. Inorganic scales formed in fracture and perforations during production of water with high salt content.
4. Organic scales formed in the fracture and perforations during production of oil with high content of heavy fractions of oil, such as paraffin wax and/or asphaltenes.
5. Insufficient transport of proppant into formation, namely, short length of proppant pack.
Nuance 1 and 2 are solved and mitigated during hydraulic fracturing design, and nuance 3 and 4 being addressed by downhole treatment in the event of production decline when impairment of well productivity is observed. If organic and inorganic scaling takes place, the scale inhibitors, in particular, paraffin wax and/or asphaltene inhibitors injected into formation during fracturing treatment may be employed. However, duration of such treatment is very short, because the chemicals injected are easily washed out from the formation and proppant pack during production stage, therefore the effectiveness of such treatments is rather low. In order to ensure high effectiveness of treatment against formation of the said scales, treating chemicals (the inhibitors) are added to the fluid at low concentrations (slightly higher than MIC, minimum inhibitor concentration) for a long period of time.
Moment 5 is related to poor transport properties of proppants in fracturing fluids. In particular, proppant settles in this fluid due to its higher density as compared to the proppant carrier fluid itself.
A decrease in proppant settling rate has been addressed in a number of patents and patent applications. Methods to decrease proppant settling rate may include the following:
1. Reduction in the effective density of particles.
2. Improved prevention of particles from settling through continuous fluid:                (a) by adding fibers and other materials into the fracturing fluid, wherein particles interact with the said fibres and settle slowly in the fracturing fluid, and        (b) by regulating the shape of proppant particles in such a way as to increase their “windage” (i. e. hydrodynamic resistance to motion of proppant particles through the fracturing fluid),which results in a lower settling rate of proppant particles in fracturing fluid and enhanced transport of proppant into a fracture.        
Some literature sources disclose the structure and application of proppants (propping agents) with a certain polymer within proppant structure or within the system which is used for reservoir treatment.
Thus, Patents Nos. RU 2441052 C2 and U.S. Pat. No. 7,931,089 B2 (Schlumberger Technology Company), being members of the same patent family, describe proppant particles, a method of their use for reservoir treatment and a method of adjusting proppant settling rate, where a proppant particle is a central portion (core) and a shell. These patents set forth that the shell may be made of polymeric fibers, polymeric sponge or other material, while the shell material softer than the particle core; however, the chemical composition of shell material is not disclosed (in particular, polymer chemistry is not specified).
U.S. Pat. No. 7,950,455 B2 discloses nonspherical particles for well treatment, filled with water-solule or oil-soluble agent(s) and a method to stimulate a formation comprising introduction of these particles into a wellbore. The particles described therein have the following modifications:                hollow cylindrical proppant particles with the dimension ratio smaller than or equal to 5.0:1.0, which can be porous or nonpopous; and        nonpopous cylindrical proppant particles with the dimension ratio smaller than or equal to 2.5:1.        
In both cases, pores and holes in particles are filled with one or more chemical treatment agent specified in depending claims of U.S. Pat. No. 7,950,455 B2. In particular, agents are selected from group: scale inhibitors, corrosion inhibitors, paraffin inhibitors, demulsifiers, gas hydrate inhibitors, flocculating agents, dispersing agents, asphaltenes and any mixtures thereof.
Patent application WO 2012/036862 A9 discloses use of polymeric particles filled by at least one functional additive for formation treatment.
Patent application PCT/US2013/074955 owned by Schlumberger discloses a method of well treatment, wherein treatment slurry includes proppant particles and peel or composite peel with particles attached thereto. The peel material is selected from the group: polylactic acids, nylons, polyhydroxyalcanoates and polycaprolactones. The largest dimension of one or more peel or composite peel is from 10 micrometers (μm) to 20 millimiters (mm).
Plate-like particles were also claimed earlier as demonstrating excellent transport properties. In particular, Patent Application PCT/RU2008/000566 (WO 2010/021563 A1), filed by Schlumberger, mentions mica as a proppant for hydraulic fracturing. Mica geometry and buoyancy allow better proppant delivery into fractures. Nevertheless, it is known from experience that mica injection into a well does not result in a hydrocarbons production increase as compared to natural sand, which is explained by lower permeability of a proppant pack created by mica.
Additionally, there are numerous patents related to chemically modified proppants with various functions of proppant itself, but without its carrying parts (carrier). Also there are patents that disclose protection from organic and inorganic scales using chemical agents-inhibitors impregnated into proppant or coated with proppant pellet inhibitors. As for long-term protection against scales, two products are commercially available, such as: ScaleGUARD® (inorganic scales) by CARBO Ceramics Inc., (Houston, Tex., USA) and ParaSorb® (organic scales) by Baker Hughes (Houston, Tex., USA).